Tanaiste Joan Burton, in an internal note to Labour Party members, has declared that the controversial Eighth Amendment on abortion "cannot be changed soon enough".
Ms Burton sent out the strident message ahead of the march in Dublin yesterday calling for the repeal of the 8th Amendment.
She wrote: "I just want to make clear the party's position on the 8th Amendment. Put simply, it is one of the most retrograde parts of the Constitution and cannot be changed soon enough.
"As a woman, it horrifies me to think of the dreadful situations fellow women and their families have been placed in because of this archaic provision.
"But pledging to repeal the 8th is the straightforward bit - replacing it with a humane, compassionate, and legislatively sound approach is the complex part. It is absolutely essential that we get this right.
"That is why I have asked Labour Women, under the stewardship of Ivana Bacik and Sinead Ahern, to bring forward a credible solution that will form the basis of our manifesto commitment.
"That commitment will be very clear - to repeal the 8th Amendment and ensure it is replaced appropriately," she added in her note.
In any subsequent programme for government negotiations, a referendum to repeal the 8th would be an absolute priority for Labour.
"Other parties will shy away from it in the election, because they don't want to deal with this very difficult and sensitive issue. That's why anybody who wishes to see the 8th repealed should vote Labour," wrote Ms Burton.
Yesterday, several thousand pro-choice campaigners lined the streets of Dublin for the fourth annual March for Choice. The rally - organised by the Abortion Rights Alliance and supported by Amnesty International Ireland - called for free, legal and safe abortion in Ireland and for an immediate referendum on repealing the 8th Amendment.
Orla O'Connor of the National Women's Council in Ireland, said abortion was a reality that the Government must accept. "It's complete hypocrisy that women's rights are still being ignored. Instead of facing the truth, they are exporting the problem," she said.
Pro-choice supporters say they will only vote for politicians who support abortion rights in the next General Election. "We are asking people to only vote for the parties that support abortion in their manifesto. It will be the first question we ask when they come knocking on our doors," said Ms O'Connor.
Dressed in Victorian-era attire, Sarah O'Toole from Galway said women's rights in Ireland were still decades behind. "We're living in the 21st Century but we are still stuck in the past on women's rights, This Government is treating us like second-class citizens. If they say no to us, we'll say no vote to them," she said.
Gary Gannon, Dublin city councillor with the Social Democrat party, said he was marching for future generations. "I'm very aware that I will never be the one to go through this, but if I ever have a daughter, I don't want her to face these barriers," he said.
Meanwhile, a spokesperson for the Pro-Life Campaign said organisers of the march were in "absolute denial regarding the hurt and heartbreak caused by abortion for many women".
Dr Ruth Cullen, of the Pro-Life Campaign said: "The pro-choice side are behaving as though they have a monopoly when it comes to the experiences of women who have had abortions."